1. Field of the Invention
The invention relates to a franking machine with at least one print head of an inkjet printing mechanism for printing flat postal objects, such as letters or postcards, inserted into or passing through the machine, comprised of a guide part arranged so as to project from the print head and relative to its jet opening plane and having correlated therewith a transport device for transporting the postal objects between it and oppositely positioned conveying rollers rotating about axes oriented transverse to the conveying direction, wherein the transport device comprises two drive rollers connected in driving connection with one another and forming together with the guide part a conveying path, which drive rollers, when viewed in the conveying direction, are arranged before and behind the print head and has a counterpressure roller arranged opposite thereto, respectively, which exerts a pressure against the drive roller or the postal object to be transported therebetween and which is reversibly liftable. The franking machines employ today in addition to the classical rotary printing technology increasingly new stamp application methods, inter alia, based on thermal or inkjet basis.
2. Description of the Related Art
It has been shown in practice that not only the print head must be replaced, but depending on the printing technology the entire franking machine configuration is subject to greater and very complex, i.e., also correspondingly expensive, changes and modifications.
Inkjet print heads have been known for quite some time and are used, in particular, in PC printers. The knowledge that has been gained for use of such print heads in this field cannot be transferred onto the present field of use in franking machines. The reasons, inter alia, lie in the high speed of the letters undergoing franking as well as their different formats and thicknesses as well as the considerably rougher conditions of the surroundings, caused partially by soiled surfaces of the postal objects. Moreover, these franking prints must fulfill strict quality requirements of the postal offices, which make necessary high construction expenditure and reliability.